Head suspension assemblies are commonly used in rigid magnetic disk drives to support magnetic heads in close proximity to the rotating disk surfaces. Head suspension assemblies of this type typically include an air bearing head slider assembly mounted to a suspension. The suspension includes a load beam having a mounting region on its proximal end and a gimbal or flexure on its distal end. When incorporated into a disk drive, the mounting region is mounted to an actuator or positioning arm, which supports the suspension assembly over the rotating disk. A baseplate is typically welded to the mounting region to increase the rigidity of the mounting region and to provide a mechanism for securely mounting the suspension assembly to the positioning arm.
The load beam is an elongated and often generally triangularly shaped member that includes a spring region adjacent to the mounting region, and a rigid region that extends from the spring region. The flexure can be manufactured as a separate member and welded to the distal end of the load beam, or formed as an integral member in the distal end of the load beam.
The air bearing head slider assembly contains a magnetic head and is typically bonded to the flexure by adhesive. The flexure allows the head slider assembly to move or “gimbal” (about rotational pitch and roll axes) with respect to the distal end of the load beam and thereby follow variations in the surface of the spinning disk. To enable the pivotal flexure movement, the surface of the flexure to which the head slider assembly is bonded is typically spaced from the adjacent surface of the load beam by structures known as load point dimples or formed offsets.
Suspensions are commonly manufactured by chemically etching flat or unformed load beam blanks from thin sheets of stainless steel. Flat and unformed flexure blanks are etched in a similar manner from sheets of stainless steel. During subsequent manufacturing operations, side rails, load point dimples and any other structures that extend upwardly or downwardly from the web or generally planar surface of the load beam are formed on the load beam blanks by mechanical bending procedures. Any dimples, offsets or other structures on the flexures requiring deformation of this type are formed in a similar manner. After forming, the flexures are welded to the distal end of the load beams. Baseplates are also welded to the suspensions following the forming operations.
The product of these etching, welding and forming operations are generally flat suspensions (i.e., the mounting region, spring region and rigid region of the load beam are generally coplanar and at the same height. During subsequent manufacturing operations, at least a portion of the spring region of the load beam is rolled around a curved mandrel or otherwise bent in such a manner as to plastically bend or permanently deform the spring region. The rolling operation imparts a curved shape to the spring region and causes the flexure to be offset from the mounting region when the suspension is in its unloaded or free state.
As noted above, the suspension supports the slider assembly over the magnetic disk. In one embodiment, air pressure at the surface of the spinning disk creates a positive pressure air bearing that causes the slider assembly to lift away from and “fly” over the disk surface. In another embodiment, a negative pressure air bearing pulls the slider assembly toward the disk surface. To counteract these hydrodynamic forces, the head suspension assembly is mounted to the disk drive with the suspension in a loaded state so the bent spring region of the suspension biases the head slider assembly either toward or away from the magnetic disk. The height at which the slider assembly flies over the disk surface is known as the “fly height.” The force exerted by the suspension on the slider assembly when the slider assembly is at fly height is known as the “gram load.”
By controlling the gram load of the head suspension, the force applied to the read/write head at a constant flying level can be determined. Current suspensions have a gram load that is determined by a bend radius in the suspension arm. The accuracy of this type of gram loading method is typically about +/−0.1 grams. Once bent into position, the suspension arm has no way of changing the gram load, unless subsequently bent or altered in a permanent way.
U.S. Pat. No. 5,898,541 (Boutaghou et al.) discloses a bi-morph piezoelectric bending motor mounted on the head slider. The bending motor cooperates with a tab surface on the flexure to rotate the slider.
U.S. Pat. No. 5,719,720 (Lee) discloses a load beam of a head suspension mechanism that has a non-load bearing, single layer of piezoelectric material on at least one surface of a resilient portion of the load beam. A controller apparatus provides a control signal to the piezoelectric material that induces expansion or contraction of the piezoelectric material to cause the load beam to raise the head slider from the surface in the disk drive. Since the piezoelectric material of the '720 patent is limited to compression and expansion forces, it must be attached directly to the surface of the load beam. Consequently, the compression or expansion of the single layer piezoelectric material occurs along the length of the load beam and must overcome the stiffness of the load beam to produce a bending or curving motion of the resilient portion of the load beam. That is, the forces generated by the compression or expansion of the piezoelectric material are parallel to the surface of the load beam. Directing the forces from the piezoelectric material parallel to the load beam limits the amount of deflection and load applied to the load beam.